I did try making those numbers larger in the grammar core, to no effect, but I do think, after trying to find an answer for you on how many polys these models are, that I might have found the problem? Here's an export log of one of these buildings (note the errors regarding the UVs):
EXPORT LOG / CityEngine 2012.1.09130547
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export started at: Wed May 08 11:30:59 2013
export completed at: Wed May 08 11:31:02 2013
export duration: 3.1 seconds
EXPORT SETTINGS
format: Autodesk® FBX® 2013
location: C:\hh\sol\CityEngine\City\models\test
base name: City_zone_E2_N1
export content: 0 (0 = models only, 1 = fallback to shape, 2 = shapes only)
file granularity: 0 (0 = single file (or split by file budget), 1 = file per initial shape)
file size budget: 0
mesh granularity: 0 (0 = as generated, 1 = mesh per material, 2 = use instances of inserted assets)
vertex precision: 0.00100
normal precision: 0.00100
texcoord precision: 0.00010
merge vertices: 1
merge normals: 1
merge texcoords: 1
triangulate: 1
reproject texcoords: 0
vertex indexing: 0 (0 = allow shared vertices, 1 = force separate vertices)
normals type: 0 (0 = use vertex normals, 1 = use face normals (flat))
normals indexing: 0 (0 = allow shared normals, 1 = force separate normals)
write texcoords: 1 (0 = no texcoords, 1 = first layer, 2 = all layers)
write materials: 1
collect textures: 1
file type: 1 (0 = ascii, 1 = binary)
embed textures: 0
write master file: 0
master group name: CityEngineSceneRoot
write cam data: 1
batch behavior: 0 (0 = normal, 1 = skip existing files, 2 = dry run)
INPUT STATS
number of initial shapes = 1
number of generated shapes = 5515
number of generated meshes = 5515
number of generated materials = 5515
OUTPUT STATS
written files: 1
written materials: 6
written meshes (total polygons): 5515 (64340)
INPUT REPORT
collected/generated initial shapes:
0: OK : Shape OID: 65d808c7-94fb-11b4-9f79-002564ace543:4
ERROR: Mesh::normalizeUV() : can not normalize, delta u is too small (0.000000)
ERROR: Rule 'Default$CityBuilding.WallTextureB;' : tileUV failed (normalize)
WARNING: Split: leaf 2 has size 0.000005, too small, ignored
ERROR: Mesh::normalizeUV() : can not normalize, delta v is too small (0.000000)
OUTPUT REPORT
written files & status:
0: OK: C:\hh\sol\CityEngine\City\models\test\City_zone_E2_N1_0.fbx
---------------
I'm thinking the shape errors are what is causing the problem? Which basically seem to be that some of the UVs are too small? Also to answer another one of your questions, I can get single buildings to export, it fails though when I try to export in groups (usually when I try to export something larger than a single city block).